This invention relates to a height control system for monitoring and adjusting the distance between a reciprocating punch marking tool and a metal plate workpiece.
Punch marking tools are often used in conjunction with welding machines or flame cutting machines in order to mark or score the workpiece so as to indicate the correct location for a future work operation such as bending or bracing.
In that the metal plate that serves as the workpiece seldom provides a perfectly even surface the distance between the tip of the punch marker and the plate surface varies. Since the length of the stroke of the reciprocating punch marker is constant the varying punch to workpiece distance results in occasions where the punch marker fails to mark the workpiece and other instances where a much deeper mark than is necessary is punched into the plate. Thus, where the distance between the punch marker and the workpiece is in excess of the optimum distance, the punch marker fails to produce a discernable indicia on the workpiece and in situations where the marker to plate distance is less than the optimum, the plate is badly deformed and the tip life for the punch is greatly reduced due to the excessive shock.
Heretofore, the distance between the punch marker and the metal plate has been monitored by sensing the electrical capacitance between the tip of the tool and the surface of the workpiece. This procedure has proven to be unreliable due to the fact that a very small capacitance is being measured and its value easily drifts when exposed to the external influences present in a welding or flame cutting environment. The known capacitance height sensing system also has required a substantial metal area in order for it to function properly. Therefore, such a system has encountered difficulties as the punch press approached the edge of the workpiece.
It is a task of the present invention to provide a punch marker height control that is impervious to the external influences present in a flame cutting or welding operation.
It is a further task of the invention to provide a height control that performs equally as well at the edge of the workpiece as in the middle of the plate.
In accordance with one aspect of the invention, a height control for a punch marker is provided and which is responsive to a timing mechanism that measures the time interval during which the marking tool is in contact with the workpiece.
In accordance with another aspect of the invention, the height control is provided with an error detection system which compares the sensed time interval with a predetermined time range that is indicative of an "in position" condition for the marking tool. The error detection system generates a correction signal upon determining that the sensed time interval is outside of the predetermined time range.
In accordance with yet another aspect of the invention, the height control is provided with a height adjustment assembly that is operable by the correction signal generated by the error detection system. The height adjustment assembly adjusts the vertical position of the punch marker relative to the workpiece in response to the correctional signal generated by the error detection system.